In a so-called Passive Optical Network or PON, a plurality of terminals are connected to a supply arm by a distribution network having a plurality of splitter junctions arranged in a tree structure. The supply arm is normally formed by a head end arranged along an optical path, and, in some cases, may include a repeater. For fault tolerance purposes, it is known to provide a back up supply arm, also connected to the distribution network. The back up supply arm duplicates the function of the main supply arm, so that if a fault occurs in the main supply arm, the back up supply arm can take over. However, in the event of such a fault, the terminals often move into a non-operational state or other fault state, and the back up supply arm is normally required to perform an initialization routine when it takes over, in order to bring the terminals back into the operational state. This can be excessively time consuming.
According to an aspect of the present invention, there is provided an optical communications system as specified in claim 1. A further aspect of the invention is specified in claim 9.